If you're looking for historical or archival research, the SDK is sometimes discussed in old gamedev forums, but any links to downloads would be unofficial and potentially unsafe or illegal.
If your goal is not to make a game but to change a Gamebryo-based game (like Oblivion or Fallout 3 ), you do not need the engine. gamebryo engine download
A "Gamebryo Engine Download" for the public does not exist. It is defunct, proprietary commercial software. If you wish to create a game, use Unreal or Unity. If you wish to mod a Gamebryo game, download the official modding tools provided by the publishers. If you're looking for historical or archival research,
Because it was a high-end professional tool used by major studios, the source code and binary files were closely guarded intellectual property. There is no free version, and any site claiming to offer a "Gamebryo crack" or "free download" is likely distributing malware or pirated, outdated, and unstable builds that will not function correctly. It is defunct, proprietary commercial software
If you are a solo developer looking for a similar "feel" or modularity without the high cost of a legacy commercial license, consider these alternatives:
The Gamebryo Engine is a game engine that was widely used in the development of games, particularly in the early 2000s. It was known for its versatility, allowing developers to create games for various platforms, including PC, Xbox, PlayStation 2, and mobile devices. The engine provided a comprehensive set of tools and features, including 3D rendering, physics, animation, and audio support.